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1. What is HeifermaX ?
HeifermaX is a medicated feed additive that suppresses
estrus or “heat” in feedlot heifers. HeifermaX alters the
animal’s reproductive cycle by preventing ovulation and, a
result stops the processes that cause the animal to come
into heat. Because it helps heifers maintain a constant,
high level of estrogen in their system, they show improved
daily gain and feed efficiency. HeifermaX contains
melengestrol acetate, a synthetic progestogen.
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2. What are the economic advantages of
using HeifermaX?
• Improved rate of gain
• Improved feed efficiency
• Shorter time to market
• More consistent performance
• Fewer riding injuries
• Fewer carcass discounts due to bruising or dark cutters
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3. Is there a pre-slaughter
withdrawal requirement for cattle fed HeifermaX?
There is no withdrawal required in the United States.
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4. Can
HeifermaX be fed in combination with other feed additives?
Yes, HeifermaX is approved to be fed with other common feed
additives. See an
updated list
of approved combinations
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5. What is the interaction between
HeifermaX and implants? Why is this synergistic?
Because HeifermaX increases the production of estrogen by
the heifers, it mimics implanting with estrogen in some
ways. Even so, effects of estrogenic implants and HeifermaX
are additive. Used together, both will provide production
and economic benefits. HeifermaX works well with trenbolone
acetate (TBA)-containing implants too. TBA stimulates muscle
growth through a different mechanism than HeifermaX so the
results are additive. In addition, most research shows
positive effects on carcass value, through increased quality
grade, when melengestrol acetate is fed to heifers that
receive TBA implants. Because HeifermaX is fed every day, it
can cover gaps in implant programs due to duration or dosage
mismatches in an implant program.
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6. Does HeifermaX work in spayed
heifers?
No, HeifermaX is effective only in intact heifers. It is not
known to have any effects in steers.
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7. What are possible reasons for
heifers being fed HeifermaX to go into heat?
There are a number of possible reasons heifers may exhibit
estrus even though they are fed HeifermaX. Improper mixing
of the supplement or feed; inadequate bunk space; exogenous
estrogens from green chop, moldy corn or hay; effects of the
weather and herd health conditions all can play a factor in
heifers exhibiting heat. In addition, normal variation in
feed consumption from day to day or from one heifer to
another, can result in individual heifers occasionally not
consuming enough HeifermaX to avoid estrus.
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8. What is the
appropriate daily intake of HeifermaX?
Diets should be formulated to provide the animal with 0.25
mg to 0.50 mg/hd/d of melengestrol acetate. Most
nutritionists and cattle feeders target consumption of at
least 0.4 mg/hd/d.
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9. What is the
difference between Type A medicated article, Type B
medicated feed and Type C medicated feed?
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10. Where can I purchase HeifermaX?
HeifermaX is distributed by micro-ingredient machine
companies and liquid supplement manufacturers. Please
contact
VetLife if you have a
question on HeifermaX availabilty.
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11. I formulate diets to result in average consumption of
0.4 mg/head/d of melengestrol acetate and yet some of my
heifers still exhibit estrus. Why?
Feedlot diets are formulated to deliver the targeted
quantity of medication to cattle with average rates of feed
consumption. As would be expected in any population,
variation exists in the amount of feed the cattle consume.
Figure 1 shows a typical distribution of
feed consumption in a population of feedyard cattle. The
highest point on the graph (most common result) is 17 lb of
dry feed consumed for the average of the feeding period.
This level of consumption occurred in about 25% of the pens.
Next most common was 18 lbs of feed consumption (about 23%
of pens). Most pens averaged between 16 lbs and 20 lbs of
dry feed consumed but a small percentage ate less than 16
lbs or more than 20 lbs.
Figure 1
These pen-to-pen differences in feed consumption result in a
distribution of consumption of medicated feed additives,
such as melengestrol acetate. An example of this is shown in
Figure 2.
Figure 2.
While the average delivery of
medication is near the target level, some pens consume
slightly more or less.
Keep in mind that these are pen averages that reflect an
entire feeding period. There will also be day-to-day
variation in feed delivery to each pen. In addition, each
pen reflects a population of cattle and consumption of
individual cattle also will vary within the pen. As a result
of all of this variation, there may be some individual
cattle that do not consume targeted levels of melengestrol
acetate on some days.
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12. What do industry
experts say about the frequency of estrus in feedyard
heifers?
There are no published data on the frequency of estrus in
feedlot heifers but it is common knowledge that some heifers
will cycle, even if they are being fed melengestrol acetate.
Industry experts with personal experience in observing
feedlot heifers have said that a common rate of estrus is
0.5% of feedyard heifers. That means that about five in
1,000 heifers would be in standing heat on any given day.
This could include some newly received heifers that have not
yet received melengestrol acetate or others on feed for a
short time.
It is important to note that not all heifers that are
exhibiting signs of restless or sexual behavior are in
estrus. Some heifers may be active but not in standing heat.
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